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LM1205N データシート(PDF) 10 Page - National Semiconductor (TI) |
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LM1205N データシート(HTML) 10 Page - National Semiconductor (TI) |
10 / 24 page Functional Description (Continued) The 0V to 4V drive control signal comes in on pin 18 Each channel has its own drive section therefore the crosstalk compensation needed for the contrast control voltages is not required for the drive control thus no external pins for the drive control The drive attenuator gives an attenuation range from 0 dB to b6 dB A small gain adjustment range for the drive attenuator is desirable and intentionally de- signed because the drive is used only to balance the overall gain of each color channel giving the correct color tempera- ture on the CRT The output of the drive attenuator stage goes to A2 the amplifier in the DC restoration section The video signal goes to the non-inverting input of A2 The inverting side of A2 goes to the output of gm1 the clamp comparator and the clamp capacitor at pin 8 During the back porch period of the video signal a negative going clamp pulse from pin 14 is applied to the clamp com- parator turning on the comparator This period is where the black level of the video signal at the output of the LM1205 LM1207 is compared to the desired black level which is set at pin 19 Figure 7 shows the timing of the clamp pulse relative to the video signal The clamp capacitor is charged or discharged by gm1 generating the correction voltage needed at the inverting input of A2 to set the video output to the correct DC level Removing the clamp pulse turns off gm1 with the correction voltage being maintained by the clamp capacitor during active video Both the clamp pulse and the blank pulse at pin 13 are TTL voltage levels There are actually two output sections bA3 and bA4 Both sections have been designed to be identical except bA4 has more current drive capability The output transistor shown is part of bA4 but has been shown separately so the user knows the configuration of the output stage bA3 does not go to the outside world it is used for feeding back the video signal for DC restoration Its output goes directly to the inverting input of the clamp comparator via the volt- age divider formed by the 500X and 4k resistors bA4 will be close to the same output as bA3 and will temperature track due to the similar design of the two output stages However the current at the output of bA4 will be ten times the current at the output of bA3 To balance both outputs a load resistance of 390X needs to be connected from pin 20 the green video output pin to ground Another input to bA4 is the blank pulse When a negative going blank pulse is applied to pin 13 the output of the LM1205LM1207 is driv- en to less than 01V above ground Using the timing shown in Figure 7 for the blank pulse the output of the LM1205 LM1207 will be less than 01V during the inactive portion of the video signal This is a ‘‘blacker than black’’ condition blanking the CRT at the cathodes By using the blank func- tion of the LM1205LM1207 no grid blanking is necessary Note that the DC restoration is done by feeding back the video signal from bA3 but blanking is done at bA4 By using the two output stages blanking can be done at the CRT cathodes and at the same time activate the DC resto- ration loop VCC1 goes to pins 3 11 and 25 (see Figure 1 ) These three pins are all internally connected For proper operation of the LM1205LM1207 it is necessary to connect all the VCC1 pins to the input power to the PCB and bypass each pin with a 01 mF capacitor VCC2 is the input power at pins 22 and 23 for the three output stages This is a separate power input from VCC1 there are no internal connections between the two different power inputs There must be a connection on the PCB between VCC1 and VCC2 Pins 22 and 23 must be bypassed by a parallel connection of a 10 mF and 01 mF capacitors The ground connections for the LM1205 LM1207 are at pins 7 21 and 24 All three ground pins are internally connected and these pins must also be connect- ed externally to a good ground plane for proper operation of the LM1205LM1207 http www nationalcom 10 |
同様の部品番号 - LM1205N |
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同様の説明 - LM1205N |
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